Apparatus for electron beam irradiation of objects

ABSTRACT

An apparatus for electron beam irradiation of objects comprises an electron beam shaper 1 providing a ribbon-shaped beam 7 and a deflecting electromagnet 8 with a frame-type magnetic circuit 9 to direct the beam 7 onto an irradiated object 6 substantially at an angle of 90°. The deflecting electromagnet 8 has two poles 10, 11 extending over the width of the irradiated object 6 and two windings 12, 13 embracing the poles 10, 11 and connected to a direct current source 14, the deflecting electromagnet 8 being arranged so that the trajectories of the electrons within the area from the shaper 1 to the deflecting electromagnet 8 are inclined to the frame of its magnetic circuit 9.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to accelerator technique, and moreparticularly to apparatus for electron beam irradiation of objects.

2. Prior Art

When objects are irradiated by charged particles, including electrons,for example, in apparatus for radiation and chemical treatment ofmaterials it is required to provide an irradiation field of considerableextension equal at least to the width of an irradiated object. The wholesurface of the object is exposed to irradiation by displacing of theobject lengthwise across the irradiation field.

Besides, the irradiation field should be uniform to providepredetermined properties of the irradiated material equal, over thewhole surface of irradiation, i.e. it is required to obtain uniformdistribution of energy of the charged particles over the surface of theirradiated object to provide equal depth of penetration of the chargedparticles into the material of the object.

Known in the art are apparatus for electron beam irradiation of objects,wherein shaping of extended irradiation fields is based on scanning ofan electron beam, i.e. on displacement of the beam of smallcross-sectional area over the irradiated surface by means of itsdeflection by a time-modulated field, most frequently by a magneticfield. In the apparatus of this type the maximum permissible width ofthe material to be irradiated depends on the vertical dimension of thevacuum chamber of the apparatus. Thus, for example, in order to sweepthe electron beam for 1 meter the vertical dimension of the vacuumchamber should be about 2 meters and further increase in the width ofthe irradiated objects considerably increases the vertical dimension ofthe apparatus. If the amount of deflection of an electron beam isincreased while maintaining the same height of the vacuum chamber,nonuniformity of the irradiation of the objects over their width occursdue to the fact that the angle of incidence of electrons onto theobjects at the extreme positions of the beam will be substantiallydifferent from the right angle corresponding to the electron trajectoryat the central beam position.

Known in the art is an apparatus for electron beam irradiation ofobjects (Cf. FRG Application No. 2,901,056 published 1979), comprisingan electron beam shaper, a deflecting electromagnet with a frame-typemagnetic circuit to direct the electron beam to the irradiated objectsubstantially at an angle of 90°, and a vacuum chamber to transport theelectron beam from the shaper through the magnetic circuit and furtherthrough an exit window of the vacuum chamber onto the surface of theirradiated object, the deflecting magnet being located wherevernecessary either outside the vacuum chamber embracing the latter, orinside the vacuum chamber. The electromagnet has a number of windingsarranged at its poles and geometrically displaced relative to oneanother along the poles. The electromagnet windings are connected inturn to a supply source through a commutator, whereby the field of theelectromagnet moves in the direction of the line equidistant to thesurface of the irradiated object.

The apparatus according to the abovementioned FRG Application eliminatesthe drawbacks inherent in the apparatus, using the scanning of anelectron beam, i.e. it can provide a uniform irradiation field ofpractically any desirable extension without increase in the height ofthe apparatus owing to horizontal arrangement of the electron beamshaper and the vacuum chamber. However, operation of the deflectingmagnet under alternating field conditions results in the followingcomplications in the apparatus design:

use of laminated magnetic circuit in the deflecting electromagnet;

use of a special commutation circuit for connecting the electromagnetwindings to the supply source, provided with a commutator controlcircuit;

when the deflecting magnet is arranged outside the vacuum chamber thelatter should either have sufficiently thin walls (0.3-0.5 mm) ofstainless steel, said walls being obligatory corrugated like belows toprovide its mechanical strength, or it should be made of dielectric suchas, for example, ceramics;

when the deflecting magnet is arranged inside the vacuum chamber it isnecessary to keep the low level of gas release within the volume of thevacuum chamber from the laminated magnetic circuit of the electromagnetand its windings, this being achieved by baking said assemblies in epoxyor other low gassing compounds with mineral fillers.

SUMMARY OF THE INVENTION

The principal object of the present invention is to provide an apparatusfor electron beam irradiation of objects, wherein an electron beamshaper and a deflecting electromagnet should be made such as to simplifythe design of the whole apparatus and to ensure uniform irradiation offlat objects of any width to be met with in practice.

With this principal object in view, there is provided an apparatus forelectron beam irradiation of objects, comprising an electron beam shaperand a deflecting electromagnet with frame-type magnetic circuit todirect an electron beam onto the irradiated object substantially at anangle of 90°, wherein, according to the invention, the electron beamshaper is made such as to provide a ribbon-shaped electron beam, thedeflecting electromagnet is made two-poled, the poles extending over thewidth of the irradiated object, and comprises two windings embracingsaid poles and connected to a direct current source, the deflectingelectromagnet being arranged so that the trajectories of the electronswithin the area from the shaper to the deflecting electromagnet areinclined to the plane of the frame of its magnetic circuit.

Two-pole deflecting electromagnet having the poles whose lengthcorresponds to the width of the irradiated object and herein proposedarrangement of the windings relative to the poles provides uniform andstationary magnetic field in the aperture of the electromagnet, wherebyall the electrons in the beam impinge onto the irradiated object at anequal angle making the irradiation field uniform over the whole width ofthe irradiated object. Due to inclination of the plane of the magneticcircuit frame of the electromagnet to the trajectories of the electronsconstituting the field produced by the electromagnet, i.e. to thelongitudinal axis of the shaper, the ribbon-shaped electron beam of theinitial width provided by the shaper is transformed into a wider beamwhile maintaining sufficient uniformity of the electron distributionover the beam cross-section, thus making it possible to obtain suitablyextended irradiation field with a reasonable height of the apparatus.

In the proposed apparatus the design of a number of assemblies issimplified, i.e. of a vacuum chamber, which can be made as athick-walled vacuum chamber of a conventional type, and of a deflectingelectromagnet whose magnetic circuit can be made all-metal, theelectromagnet supply circuit being simplified as well.

According to one embodiment of the present invention the electron beamshaper comprises an electron gun with an extended cathode and anaccelerating tube providing acceleration of the ribbon-shaped electronbeam.

In this case the shaping of the ribbon electron beam is provided by theshaper comprising minimum number of elements.

According to another embodiment of the present invention the electronbeam shaper comprises an electron gun with a point cathode, anaccelerating tube, an electron beam sweeping electromagnet, and acorrecting electromagnet arranged along the path of the electrons nextto a sweeping electromagnet for orientation of the electron trajectoriesin the direction coinciding with their direction at the exit from anaccelerating tube.

In this case the electron beam shaper can comprise the elements whosemanufacturing process is well developed in the accelerator technique.

The present invention will subsequently be more apparent from thedetailed description of its embodiments taken in conjunction with theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an apparatus for electron beam irradiation ofobjects, according to the invention, with a partial cross-section of avacuum chamber and a deflecting electromagnet;

FIG. 2 is a top view of the apparatus shown in FIG. 1;

FIG. 3 shows one embodiment of an electron beam shaper of the apparatusshown in FIGS. 1 and 2 according to the invention; and

FIG. 4 shows another embodiment of an electron beam shaper of theapparatus shown in FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus for electron beam irradiation of an objects comprises anelectron beam shaper 1 (FIG. 1) connected through an electron conduit 2with a vacuum chamber 3 provided with an exit window 4 made of a foiland fixed on the vacuum chamber 3 with a flange 5. Located under theexit window 4 is an object 6 to be irradiated by electrons, e.g. a film,a lacquer coating or a cloth. According to the invention, the shaper 1provides, by one of the particular ways described below, a ribbon-shapedelectron beam 7, i.e. such a beam one of whose cross-sectionaldimensions is many times more than its other dimension. In FIG. 1 thegreatest dimension of the cross-section of the electron beam lies in theplane of the drawing, whereas the smallest dimension lies in thedirection perpendicular to the plane of the drawing. FIG. 1 shows theelectron beam shaper 1 schematically, i.e. it does not show the elementsconstituting this shaper forming the ribbon-shaped electron beam, andthe beam 7 itself is shown slightly diverging in the vertical plane,that corresponds to the most general case of shaping of electron beams,including ribbon-shaped electron beams, wherein natural divergence isnot eliminated, or to the scanning at a small angle (±5°) of the focusedelectron beam.

The apparatus comprises also an electromagnet 8 with a frame-typemagnetic circuit 9, embracing the vacuum chamber 3 and designed todirect the electron beam shaped by the shaper 1 to the irradiated object6 at an angle of 90°. According to the invention, the deflectingelectromagnet 8 is arranged so that the electron trajectories within thearea extending from the shaper 1 to the deflecting electromagnet 8 beinclined to the plane of the frame of its magnetic circuit 9. Thedeflecting electromagnet 8 has two poles 10 (FIG. 2) and 11 arrangedalong the long sides of the magnetic circuit 9, and two windings 12 and13 embracing the poles 10 and 11 respectively, and connectedelectrically in series and in accordance. The windings 12 and 13 areconnected to a direct current source 14 (FIG. 1). The length of thepoles 10 (FIG. 2) and 11 is slightly greater than the maximum width ofthe irradiated object 6, to be met with in practice.

Though FIG. 2 shows the deflecting magnet 8 with salient poles 10 and 11it is evident that the poles of the electromagnet 8 may not be salient,i.e. the magnetic circuit 9 may not have inward projections, the polesof the electromagnet 8 being formed in that case by the parts of themagnetic circuit situated between each of the windings 12 and 13.

FIG. 3 illustrates one of the embodiments of the proposed apparatus, thedeflecting electromagnet 8 being schematically shown in the form of atriangle limiting the zone of the magnetic field produced by theelectromagnet, whose lines of force are perpendicular to the plane ofthe drawing and are designated by the crosses. According to thisembodiment the electron beam shaper comprises an electron gun 15 with anextended heated cathode 16 supplied with the heat current throughterminals 17. The electron gun 15 is arranged inside a highvoltageelectrode 18 coupled to an accelerating tube 19 and connectedelectrically via through insulator 20 and a terminal 21 to anaccelerating-voltage source (not shown). The accelerating tube 19 withthe electron gun 15 is arranged inside a sealed housing 22 filled withelectroinsulating medium, for example, transformer oil.

The accelerating section of the accelerating tube 19, consisiting ofelectrodes 23 and insulators 24, has such an outline in thecross-section perpendicular to the beam 7, that it provides accelerationof the ribbon-shaped beam 7 produced by the extended cathode 16 withpractically parallel electron trajectories.

FIG. 4 shows another embodiment of the proposed apparatus, wherein theelectron beam shaper 1 comprises an electron gun 25 with a point cathode26, and an accelerating tube 27 with such an outline of the acceleratingelectrodes 28 and insulators 29 which provides acceleration of theelectron beam focused in the cross-section produced by the point cathode26. In other words, the accelerating tube 27 presents in this particularcase a well known type of accelerating tube with circular acceleratingelectrodes and insulators widely used in the accelerator technique. Inorder not to complicate the drawing a part of the vacuum chamber 3, thedeflecting electromagnet and the irradiated object are not shown in FIG.4.

The electron beam shaper 1 also comprises a sweeping electromagnet 30arranged on the electrone conduit 2, and a correcting electromagnet 31located along the path of the electrons next to the sweepingelectromagnet 30. Windings 32 of the sweeping electromagnet 30 areconnected to a sweep current generator 33. The correcting electromagnethas two pairs 34 and 35 of wedge shaped poles, the windings 36 and 37 ofthe correcting electromagnet 31 being connected electrically in seriesand in opposition and coupled to a direct current source 38. Thecorrecting electromagnet 31 is used to change the direction of theelectrons deflected by the sweeping electromagnet 30 so that thetrajectories of all the electrons in the beam 7 be parallel to theirinitial trajectory at the exit from the accelerating tube 27.

The proposed apparatus operates as follows.

The shaper 1 (FIG. 1) provides the ribbon-shaped electron beam slightlydiverging in the vertical plane. When the current flows from the source14 through the windings 12 and 13 of the electromagnet 8 the stationaryuniform magnetic field is excited within the interpole space thereof,the lines of force of said field piercing through the vacuum chamber 3in the direction perpendicular to the plane of the electron beam 7. Thedirection of the lines of force of the field of the electromagnet 8 isshown in FIG. 2 by arrows.

The electrons incident to this magnetic field move circlewise, theradius of this circle being determined by their energy and the intensityof the magnetic field, and are deflected from their initial trajectoriesin the direction to the irradiated object 6, the uniformity of thedistribution of the electrons over the cross-section of the beam 7 beingkept equal to the uniformity of the initial ribbon beam shaped by theshaper 1. By adjusting of the exciting current flowing through thewindings 12 and 13 of the electromagnet 8, the width of its poles 10 and11 (FIG. 2) and electron energy being pre-assigned, the direction of thecentral trajectories in the beam 7 (FIG. 1) to the irradiated object atan angle of 90° is obtained. It is evident that divergence of electronsin the beam 7 will remain also after the deflection thereof by themagnet 8, as a result of which the extreme electrons in the beam 7 willstrike the irradiated object at an inclined direction, but since thedivergence of the electron trajectories in the beam does not exceed ±5°this inclination is small enough and practically does not affect theuniformity of irradiation of the objects. Therefore, it may beconsidered to be sufficiently accurate for practice, that the electronsfall onto the irradiated object 6 at an angle of 90°.

The deflection of the trajectories of the electrons produced by theelectromagnet 8 results in the increase in the width of theribbon-shaped beam 7 from relatively small dimension limited by theconstructional peculiarities of the elements of the shaper 1 to thewidth of the irradiated object 6.

In the embodiment shown in FIG. 3 the shaper 1 forms a ribbon-shapedelectron beam 7 with practically parallel trajectories of the electrons,the width of the electron beam 7 being equal to the length of thecathode 16. In this case all the electron trajectories have the sameinclination to the plane of the aperture of the electromagnet 8 and willbe deflected onto the object in an identical way.

The apparatus, as best shown in FIG. 4, operates in a similar mode,except for the fact that at the exit of the accelerating tube 27 thereis formed a "linear", i.e. focused in the cross-section, beam which isscanned by an alternating magnetic field generated by the sweepingelectromagnet 30 within the aperture of the correcting electromagnet 31.Between each pair 34 and 35 of the poles of the electromagnet 31 astationary magnetic field is excited whose intensity decreases towardsthe center of the beam, the direction of the lines of force of themagnetic field between the poles 34 being opposite to the direction ofthe lines of force of the magnetic field between the poles 35. Due tosuch an outline of the field of the correcting electromagnet 31 theelectrons far removed from the center of the beam are deflected by theelectromagnet 31 to a greater angle, and the electrons on differentsides from the centre of the beam are deflected in different directions,whereby the trajectories of all the electrons passed through the fieldof the correcting electromagnet 31 are found to be parallel to oneanother and to their initial trajectory at the exit from theaccelerating tube 27.

COMMERCIAL APPLICABILITY

The present invention may be used in radiation and chemical tecknologywhen designing the apparatus for different kinds of tecknologicalprocesses: treatment of polymeric films, lacquer coatings, textilematerials. The invention allows to design an apparatus with betterweight-to-dimension parameters providing the possibility of using localbiological protection of the apparatus. It has to be noted herewith thatsuch apparatus can be used without any special measures in the rooms,wherein technological operations not connected with radiation treatmentare carried out.

The advantage of the invention as compared to known apparatus of similardesignation is in combination of such properties as the simplicity inconstruction and small height (1.5 meter) thereof, which substantiallyfacilitates the operation of the apparatus. The apparatus in accordancewith the invention can irradiate the objects of any width to be met within practice with sufficient radiation doze homogeneity.

We claim:
 1. An apparatus for an electron beam irradiation of objects,comprising an electron beam shaper and a deflecting electromagnet with aframe-type magnetic circuit to direct the electron beam onto anirradiated object substantially at an angle at 90°, characterized inthat the electron beam shaper 1 is made such as to provide aribbon-shaped electron beam 7, the deflecting electromagnet 8 havingtwo-poles 10, 11, said poles extending over the whole width of theobject 6, and comprises two windings 12, 13 embracing said poles 10, 11and connected to a direct current source 14, the deflectingelectromagnet 8 being arranged so that the trajectories of the electronswithin the area from the shaper 1 to the deflecting electromagnet 8 areinclined to the plane of the frame of its magnetic circuit 9, andwherein the electron beam shaper 1 comprises an electron gun 15 with anextended cathode 16 and an accelerating tube 19 providing accelerationof the ribbon-shaped electron beam.
 2. An apparatus as set forth inclaim 1, further comprising a correcting electromagnet 31 located alongthe path of the electrons next to the sweeping electromagnet 30 toorient the trajectories of the electrons in the direction coincidingwith their direction at the exit from the accelerating tube
 27. 3. Anapparatus for irradiation, comprising an electron beam shaper and adeflecting electromagnet with a frame-type magnetic circuit to directthe electron beam onto an irradiated object substantially at an angle of90°, the electron beam shaper is made such as to provide a ribbon-shapedelectron beam, and the deflecting electromagnet has two poles, saidpoles extending over the whole width of the irradiated object andcomprises two windings connected to a direct current source, thedeflecting electromagnet being arrangeed so that the trajectories of theelectrons within the area from the shaper to the deflectingelectromagnet are inclined to the plane of the frame of its magneticcircuit, characterized in that the electron beam shaper (1) comprises anelectron beam (25) with a point cathode (26), an accelerating tube (27)and an electron beam sweeping electromagnet (30).